add feature to include pagination links in response

.gitignore

@@ -19,3 +19,4 @@ test/version_tmp
 tmp
 *.swp
 .ruby-version
+.ruby-gemset

README.md

@@ -273,6 +273,18 @@ And you can change the JSON key that the serializer should use for a particular
 The `url` declaration describes which named routes to use while generating URLs
 for your JSON. Not every adapter will require URLs.
 
+## Pagination
+
+If you want pagination links in your response, specify it in the `render`
+
+```ruby
+  render json: @posts, pagination: true
+```
+
+AMS relies on either Kaminari or WillPaginate. Please install either dependency by adding one of those to your Gemfile.
+
+Pagination links will only be included in your response if you are using an Adapter that supports `root`, as JsonAPI and Json adapters, the default adapter (FlattenJson) doesn't have `root`.
+
 ## Caching
 
 To cache a serializer, call ```cache``` and pass its options.

lib/active_model/serializer/adapter.rb

@@ -21,9 +21,9 @@ module ActiveModel
       end
 
       def as_json(options = nil)
-        hash = serializable_hash(options)
-        include_meta(hash)
-        hash
+        serializable_hash(options).tap do |hash|
+          include_meta(hash)
+        end
       end
 
       def self.create(resource, options = {})
@@ -94,6 +94,21 @@ module ActiveModel
         json[meta_key] = meta if meta
         json
       end
+
+      def include_pagination_links(json)
+        return unless page_links
+
+        links?(json) ? json.merge!(page_links) : json['links'] = page_links
+        json
+      end
+
+      def page_links
+        @links ||= serializer.page_links
+      end
+
+      def links?(json)
+        !json['links'].nil?
+      end
     end
   end
 end

lib/active_model/serializer/array_serializer.rb

@@ -4,8 +4,9 @@ module ActiveModel
       NoSerializerError = Class.new(StandardError)
       include Enumerable
       delegate :each, to: :@objects
+      delegate :page_links, to: :pagination
 
-      attr_reader :root, :meta, :meta_key
+      attr_reader :root, :meta, :meta_key, :pagination
 
       def initialize(objects, options = {})
         @root = options[:root]
@@ -24,6 +25,7 @@ module ActiveModel
         end
         @meta     = options[:meta]
         @meta_key = options[:meta_key]
+        @pagination = ActiveModel::Serializer::Pagination.new(objects) if options[:pagination]
       end
 
       def json_key

lib/active_model/serializer/pagination.rb

@@ -0,0 +1,63 @@
+module ActiveModel
+  class Serializer
+    class Pagination
+      attr_reader :collection
+
+      def initialize(collection)
+        @collection = collection
+      end
+
+      def page_links
+        send(default_adapter)
+      end
+
+      private
+
+      def kaminari
+        build_links collection.size
+      end
+
+      def will_paginate
+        setup_will_paginate
+        build_links collection.per_page
+      end
+
+      def build_links(per_page)
+        pages = pages_from.each_with_object({}) do |(key, value), hash|
+          hash[key] = "?page=#{value}&per_page=#{per_page}"
+        end
+        { pages: pages } unless pages.empty?
+      end
+
+      def pages_from
+        return {} if collection.total_pages == 1
+
+        {}.tap do |pages|
+          unless collection.first_page?
+            pages[:first] = 1
+            pages[:prev]  = collection.current_page - 1
+          end
+
+          unless collection.last_page?
+            pages[:next] = collection.current_page + 1
+            pages[:last] = collection.total_pages
+          end
+        end
+      end
+
+      def default_adapter
+        return :kaminari if defined?(Kaminari)
+        return :will_paginate if defined?(WillPaginate::CollectionMethods)
+        raise "AMS relies on either Kaminari or WillPaginate." +
+          "Please install either dependency by adding one of those to your Gemfile"
+      end
+
+      def setup_will_paginate
+        WillPaginate::CollectionMethods.module_eval do
+          def first_page?() !previous_page end
+          def last_page?() !next_page end
+        end
+      end
+    end
+  end
+end

lib/active_model_serializers.rb

@@ -2,6 +2,7 @@ require 'active_model'
 require 'active_model/serializer/version'
 require 'active_model/serializer'
 require 'active_model/serializer/fieldset'
+require 'active_model/serializer/pagination'
 require 'active_model/serializable_resource'
 
 begin